Mercury vapor lamp utilizing a combination of phosphor materials

Abstract

Color correction is provided in a high-pressure mercury vapor discharge lamp with a particular combination of two different phosphor materials producing an efficient composite emission. A blend of said phospor materials can improve color rendition without effecting any significant reduction in the lamp lumen output.

What I claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. In a high-pressure mercury vapor lamp comprising an inner discharge assembly including an arc tube containing a filling of mercury, a transparent outer envelope surrounding said discharge assembly and spaced therefrom, and a phosphor coating deposited on the inner surface of said outer envelope, the improvement which comprises using a phosphor blend of a red-emitting phosphor selected from the group consisting of europium-activated yttrium vanadate and europium-activated yttrium vanadate phosphate with up to about 30 weight percent in said phosphor blend of cerium-activated yttrium aluminate phosphor so as to absorb at least part of the 436 nanometer emission generated by the mercury arc discharge. 
     
     
       2. A lamp as in claim 1 wherein the cerium-activated yttrium aluminate phosphor has the general formula:   (Y.sub.1.sub.-x) Ce.sub.x).sub.3 Al.sub.5 O.sub.12     with x having an approximate value in the range 0.004 to 0.020.   
     
     
       3. A lamp as in claim 2 wherein x has an approximate value in the range 0.004 to 0.005. 
     
     
       4. A lamp as in claim 2 wherein the weight percent of the cerium-activated yttrium aluminate phosphor in the phosphor blend is in the approximate range 5-30. 
     
     
       5. A lamp as in claim 1 wherein the phosphor blend is a mixture of said cerium-activated yttrium aluminate phosphor with europium-activated yttrium vanadate phosphate phosphor. 
     
     
       6. A lamp as in claim 1 wherein the color rendering index has been increased without significant reduction in the lamp lumen output. 
     
     
       7. A lamp as in claim 1 wherein the arc tube contains a pair of spaced apart principal electrodes and an auxiliary electrode disposed adjacent one of said principal electrodes. 
     
     
       8. In a high-pressure mercury vapor lamp comprising an inner discharge assembly including an arc tube having a pair of spaced apart principal electrodes and an auxiliary electrode disposed adjacent one of said principal electrodes, a filling of mercury and inert gas within said arc tube, a transparent other envelope surrounding said discharge assembly and spaced apart therefrom, and a phosphor coating deposited on the inner surface of said outer envelope, the improvement which comprises using a phosphor blend to improve the color rendering index without significant reduction in the lamp lumen output, said phosphor blend comprising a mixture of europium-activated yttrium vanadate phosphate phosphor and approximately 5-30 weight percent of a cerium-activated yttrium aluminate phosphor having the general formula:   (Y.sub.(1.sub.-x) Ce.sub.x).sub.3 Al.sub.5 O.sub.12     with x having an approximate value in the range 0.004 to 0.020 so as to absorb at least part of the 436 nanometer emission generated by the mercury arc discharge.   
     
     
       9. A lamp as in claim 8 wherein the cerium-activated yttrium aluminate phosphor further contains excess alumina. 
     
     
       10. In a high-pressure mercury vapor lamp comprising an inner discharge assembly including an arc tube containing a filling of mercury, a transport outer glass envelope surrounding said discharge assembly and spaced therefrom, and a phosphor coating deposited on the inner surface of said outer envelope, the improvement which comprises having a phosphor blend layer of a red-emitting phosphor with up to about 30 weight percent in said phosphor blend of cerium-activated yttrium aluminate phosphor so as to absorb at least part of the 436 nanometer emission generated by the mercury arc discharge overlying an alumina ultraviolet reflecting underlayer, said alumina underlayer comprising vapor-formed spherical alumina particles having an individual particle size range from approximately 400 Angstroms to 5,000 Angstroms in diameter and said underlayer scattering at least 99 percent of the incident radiation with minor lumen loss when deposited directly upon the clear internal surface of the outer glass envelope. 
     
     
       11. A lamp as in claim 10 wherein the alumina underlayer has a thickness providing selective ultraviolet reflection without significantly reducing visible transmission. 
     
     
       12. A lamp as in claim 10 wherein the cerium-activated yttrium aluminate phosphor has a general formula:   (Y.sub.(1.sub.-x) Ce.sub.x).sub.3 Al.sub.5 O.sub.12     with x having approximate value in the range 0.004 to 0.020.   
     
     
       13. A lamp as in claim 12 wherein x has an approximate value in the range 0.004 to 0.005. 
     
     
       14. A lamp as in claim 10 wherein the weight percent of the cerium-activated yttrium aluminate phosphor is in the approximate range 5-30. 
     
     
       15. A lamp as in claim 10 wherein the phosphor blend is a mixture of said cerium-activated yttrium aluminate phosphor with europium-activated yttrium vanadate phosphate phosphor. 
     
     
       16. A lamp as in claim 10 wherein the color rendering index has been increased without significant reduction in the lamp lumen output.